1. Field of the Invention
The present invention relates to techniques for controlling communication between a movable station that is provided in a device and that moves and a fixed station.
2. Description of the Related Art
In the field of industrial devices, the development of cell-production robots, in which a single robot is capable of performing multiple types of operations, has been advancing. Such robots are comprised of an arm that is used for all tasks and an end effector that corresponds to an area from the wrist down. Multiple types of end effectors are prepared based on the type of each task, and the robot automatically exchanges end effectors depending on the type of the task, such as welding, gripping, tightening screws, and so on. There are some end effectors capable of executing advanced processes, such as capturing a processing target using a mounted camera, performing image processing on the captured image, and selecting and gripping a single component from among mixed components using the result of the image processing. In the case where control is carried out based on image processing, the processor that performs that processing is required to have high processing capabilities, and such processors can be large, and can also act as heat sources. For example, in precision machining applications, the expansion and contraction of processing targets, end effector components, and so on due to heat can quickly become problematic; thus such processors are often disposed in locations distanced from the robot, and remotely control the robot using a communication cable.
Meanwhile, in addition to being detachable as mentioned earlier, it is generally required that end effectors are capable of changing angle, orientation, and so on relative to the arm. Accordingly, it is necessary for a communication cable used to acquire images from and control an end effector to have a special mechanism for accommodating detachment, deformation, and so on. Such mechanisms have high costs, and also carry a risk of degradation and disconnection due to the cable repeatedly deforming; there is consequently an increased need to control end effectors through wireless communication.
However, wireless communication techniques widely used in the field of mobile information terminals, such as wireless LAN (local area network) and the like, are generally difficult to employ in the aforementioned applications. This is because industrial devices are required to transmit uncompressed images, transmit control data with extremely low latency, and so on. Wireless LAN and the like were not designed with such applications in mind, and thus do not meet the demands of industrial devices.
Meanwhile, high-frequency wireless communication systems such as 60 GHz-band millimeter waves can be used for wireless communication systems for the aforementioned applications. Such wireless communication systems are capable of ensuring bandwidths of 1 Gbps or more, and are thus capable of transmitting uncompressed images. Furthermore, by using appropriate communication protocols, such systems are also capable of transmitting control data at low latency. However, even in the case where it is necessary to transmit uncompressed image data but it is not necessary to transmit control data at low latency, there are cases, due to issues such as device size and heat, where it is difficult to use separate communication systems, such as using millimeter wave communication to transmit image data and wireless LAN to transmit control data.
It is typically more difficult to ensure reliability in wireless communication than in wired communication. One reason for this is that wireless communication is susceptible to shielding of and reflections from obstacles, noise from surrounding sources, and so on. End effectors not only constantly change position, orientation, and so on as the arm moves, but also operate in environments where other apparatuses are moving in the periphery, and thus ensuring reliability when employing wireless communication to control robots is an issue.
A system that uses a plurality of fixed stations is known as a technique for improving the reliability of wireless communication. For example, Japanese Patent Laid-Open No. 2010-135982 discloses a technique that improves the reliability of communication by switching among a plurality of fixed stations in time-division and communicating with a movable station to obtain a spatial diversity effect. Japanese Patent Laid-Open No. 2000-307507, meanwhile, discloses a technique that improves the reliability of communication by acquiring location information detected by a movable station and using the fixed station that is closest to that location.
If an end effector is thought of as a movable station and a remote control apparatus is thought of as a fixed station, a system that controls a cell-production robot by providing a plurality of fixed stations in the vicinity of an arm and communicating wirelessly with a movable station installed in the end effector at the end of the arm can be considered. Because communications with high capacity and low-latency are carried out, it is assumed here that millimeter wave wireless communication is used. High-frequency electromagnetic waves such as millimeter waves, submillimeter waves, and so on have a high degree of straightness, and have a property in which communication is difficult, even at short distances, in a non line-of-sight environment. Typically, a large number of components, platforms on which the components are placed, and so on are present in environments in which cell-production robots operate, and thus transmission paths between each fixed station and the movable station frequently fall into the non line-of-sight condition.
Meanwhile, even if the line-of-sight can be ensured, there are cases where communication fails due to reflections from nearby objects, noise, and so on. In order to prevent such communication failures, performing redundant communication by using a plurality of fixed stations that can ensure lines of sight can be considered. However, with conventional techniques, it has not been possible to automatically perform such communication control in accordance with arm operations. As a result, there has been a problem in that in some cases, the communication reliability necessary for robot control cannot be ensured, and it is thus necessary to carry out hard-wired control, incurring high costs as a result.
Having been achieved in light of the aforementioned problem, the present invention provides a technique for improving the reliability of communication in a wireless communication system using a simple configuration.